Spies with surveillance agencies in the United States and United Kingdom may have spent time undercover as orcs and blood elves, infiltrating video games like "World of Warcraft" in a hunt for terrorists "hiding in plain sight" online.

Agents from the CIA, FBI and Pentagon and England's Government Communications Headquarters infiltrated WoW and virtual world "Second Life," as well as collecting information on the Xbox Live gaming network, according to the documents.

None of the newly leaked documents, published this time in conjunction with ProPublica and the New York Times, mentioned specific terrorist activity foiled via the projects.

But apparently so many agents were engaged in playing video games for national security that a "deconfliction" group was created to make sure government agents weren't accidentally spying on each other.

Unlike traditional console and desktop games in which players compete in a closed environment, massively multiplayer online games (MMOs) allow players from around the world to team up and play together, often in real time using in-game communication tools.

"World of Warcraft" is the most popular online role-playing game ever. It peaked at about 12 million subscribers in 2010 and still has more than 7 million, according to Blizzard.

It's unclear whether the agencies had surveillance capabilities within the massively multi-player games that normal players would not. A spokesman for Blizzard Entertainment, which owns "World of Warcraft," told The Guardian it is unaware of any surveillance having taken place.

"If it was, it would have been done without our knowledge or permission," the spokesman said.

"Obviously online games which include chat or IM facilities do provide a method for people to communicate ... but how practical is it to have a team of spies sniffing around 'World of Warcraft' to see what they might find?" he wrote.

"Why aren't they also snooping -- maybe they are! -- on the chess app I have on my smartphone? Perhaps every time I mess up my Dutch Stonewall defence it's not really an indication that I'm a lousy chess student, but instead a coded message for my opponent to launch an attack on SCADA systems in the Netherlands?"

Snowden, 30, has admitted he was the source behind the leak of classified NSA documents, which revealed the existence of top-secret surveillance programs that collect records of domestic e-mails and telephone calls in the United States and monitor the cell phone and Internet activity of overseas residents.

A former contractor with the agency, he is wanted in the United States on espionage charges.